Show Hints / Candidates will help you see the available pencil values within the cell, row, column, and boxes.

Sudoku How To Technique: Naked Triple

Extending the rule of Naked Pair it uses the concept of “it has to be one of these three, therefore it can’t be anywhere else within that block”, but with an additional twist of the three valid cells do not need to have all of the three unique hints. You can see in the diagram that CELL R5C3 {1,2}, and R5C8 {1,9} both only have two hints. With the addition of the HINTS found in R5C9 {1,2,9} you will find between all three cells you have a total combination of three unique possible HINTS within one sharing BLOCK R5. This allows us to know that CELLS R5C4 and R5C5 can no longer have HINT values of {1,2,9}. This same concept applies to Naked Quad and Naked Quint hit reduction methods.